In response to RFA MH-94-O09, we propose to collect two annual waves of data on a nationally-representative household sample of 7000 children and adolescents ages 4 through 17 years. These data will allow us to estimate the prevalence and incidence of mental disorder and to study patterns of mental health service utilization, barriers to service use, and the costs and financing of mental health services in the U.S. Reliable and valid computer-assisted structured diagnostic interviews and interviews regarding services and related factors will be conducted by professional lay interviews in the homes of eligible youths. Due the broad age range of the sample, different pairs of developmentally-appropriate informants (adult caretaker and teacher, or caretaker and youth) will be interviewed at different ages. We will interview all three informants at some ages, however, to distinguish between changes in age and changes in informants. Annual in-person assessments will be supplemented by interim telephone assessments of service use and level of functioning and by a survey of service providers. Youths of Hispanic and African-American heritage will be oversampled to assess possible biases in access to services. We also will compare rates of mental disorder and service use across age, gender, socioeconomic levels, degree of acculturation and ethnic identity, and degree of urbanicity in controlled analyses. In addition, we will follow a subsample of 3500 youths with mental disorders and/or mental health service use over a longer period to study the stability of mental disorder, pathways to and through service use, barriers and determinants of services, costs of services, and outcomes of services. The UNO-CAP National Survey will allow the testing of numerous important hypotheses regarding mental disorder and mental health services in a longitudinal sample that will be unprecedented in terms of representativeness and statistical power. Not only will the UNO-CAP study lead to immediate improvements in the data base for mental health policy for youths, but will facilitate future research by answering key questions and providing a powerful multi-use data set for the study of mental disorder and the optimal allocation of service resources.